The present invention relates to a biological information monitoring apparatus which displays biological information that is obtained by processing a detection signal detected from a living body, on a displaying unit, which generates an alarm sound through a speaker, or which lights an alarm lamp in an alarm indicator configured by LEDs and the like, and particularly to a biological information monitoring apparatus which can output a visual alarm and auditory alarm in which the alarm priority of a vital alarm that is to be output when there is an abnormality of the detected signal, or that of a technical alarm that is to be output when there is an abnormality of the biological information monitoring apparatus, a sensor, or the measurement environment is changed depending on the situation. The invention relates also to an alarm control method.
As an example of a patient monitoring apparatus, the following configuration is disclosed in JP-A-2009-101214.
A typical pulse oximeter measures two biological parameters (the present oxygen saturation (hereinafter, often abbreviated as sat) of blood hemoglobin, and the pulse rate (hereinafter, often referred to as rate)). For alarm purposes, normal ranges which are preferably maintained in the patient are determined, and low and high thresholds are set for both the sat and the rate. In the case of a neonatal infant, for example, the sat is preferably maintained between 80 and 95 percent, and the rate is preferably maintained in the range of 90 to 190 beats/minute.
From the two measured parameters, four alarm types (low sat, high sat, low rate, and high rate) are produced. In a typical pulse oximeter, when one of the sat and the rate goes outside the normal range, an alarm is immediately output, and, when both the sat and the rate return within the normal range, the alarm is immediately ended. Typically, an alarm is in the form of an auditory sound and/or visual indicator.
Each occurrence in which a measured parameter goes outside the normal range is referred to as an event. In a typical pulse oximeter, namely, each event corresponds to an alarm, and the time duration of the alarm coincides with the time duration of the event.
Usually, many alarms generated by a typical pulse oximeter are not considered so as to correspond to events which are clinical effective.
The definition of clinical effectiveness varies depending on the patient and the environment. Usually, it is related to the severity and time duration of the event of interest. For example, a very shallow desaturation is considered effective only when sustained for a relatively long time duration.
Similarly, a desaturation of a very short duration is considered effective only when it falls very deep below the low sat threshold. Moreover, a parameter measurement error due to noise or signal artifact produces a false event. Any alarm which corresponds to a clinically effective event is considered a nuisance alarm.
Studies which attempt to reduce the number of saturation alarms have been announced. These studies are directed to lowering of the alarm threshold or waiting of a certain fixed time duration after the threshold is passed.
Lowering of the alarm threshold is problematic because the oxygen saturation of the patient indefinitely remains below the original threshold (which is higher than the new threshold), and an alarm is not produced.
Delaying of the production of an alarm by a fixed time period is also problematic because of a potentially serious situation in which the oxygen saturation of the patient abruptly falls to or remains at a very low level at which prompt medical treatment is required.
Therefore, the disclosed subject matter provides a method and apparatus for controlling an alarm in a medical diagnostic apparatus in which an alarm is produced when a measured value of a biological parameter passes a threshold.
In the disclosed subject matter, both the time amount for which the measured value passes the threshold, and the amount by which the measured value passes the threshold are determined or quantized). An alarm is inhibited based on a combination of the time amount and the amount by which the threshold is passed. Preferably, the combination is an integral or some integral functions.
In a preferred embodiment, for a saturation alarm of a pulse oximeter, the integral of the amount by which the oxygen saturation exceeds an upper threshold or falls below a lower threshold is calculated. When the integral exceeds a predetermined value, the saturation alarm is produced.
For a rate alarm of a pulse oximeter, similarly, the preferred embodiment calculates the integral of the amount by which the pulse rate exceeds upper and lower thresholds. When the integral exceeds a predetermined value, the rate alarm is produced.
As an alarm standard for a biological information apparatus (medical electrical equipment (“ME”) apparatus), international IEC 60601-1-8 is set. A summary of the standard will be described.
Table 1 shows alarm condition priorities in the standard of IEC 60601-1-8.
It is assumed that alarm conditions are assigned to one or more of a high priority, a medium priority, and a low priority. The priority is determined based on the risk management process (ISO 14971) shown in Table 1. The alarm condition priorities must be shown in an operation manual, and the priorities may be identified in a group.
Table 2 shows visual alarm signals in the standard of IEC 60601-1-8.
In the case where an alarm indicator is necessary for the operator to identify an apparatus or part of the apparatus which requires a response or awareness by the operator, characteristics such as shown in Table 2 are provided.
Tables 3(a) and 3(b) show alarm sounds (auditory alarms) in the standard of IEC 60601-1-8.
Table 4 shows melody alarms in auditory alarms in the standard of IEC 60601-1-8.
An alarm system which emits an alarm sound must have at least one of the following sets (1) and (2):
(1) the priority is patterned, and adapted to Tables 3(a) and 3(b); and
(2) the alarm is generated by a different technique (such as an audio alarm signal), and the adequacy thereof is confirmed.
In Table 4, when the absolute frequency of [c] is between 150 to 500 Hz, sound can be produced by a different key. For auditory alarm signals of all alarm systems, “normal” burst can be used. In Table 4, c, d, e, f, g, a, b, and C are musical relative pitches, and C is higher than c by one octave. An alarm signal of the high priority is generated by the five indicated pulses, and repeated once so that a total of ten pulses are obtained.
TABLE 1Alarm condition priorityPotential result when fail toGeneration of potential injuryrespond to cause of alarm stateImmediateRapidLateDeath or irreversible injuryHigh priority (H)High priority (H)Medium priority (M)Reversible injuryHigh priority (H)Medium priority (M)Low priority (L)Minor injury or unpleasantMedium priority (M)Low priority (L)Low priority (L) orfeelingnon-alarming signal
TABLE 2Characteristics of light of alarm indicatorColor ofBlinkOperationClass of alarmindicator lightfrequencyperiodHigh priority (H)Red1.4 to 2.8 Hz20 to 60% arein lit stateMedium priority (M)Yellow0.4 to 0.8 Hz20 to 60% arein lit stateLow priority (L)Cyan or yellowConstant100% are(lit state)in lit state
TABLE 3(b)Burst characteristics of auditory alarm signalAlarm signal ofAlarm signal ofAlarm signal ofCharacteristicshigh prioritymedium prioritylow priorityPulse number of burst1031 or 2Spacing between pulses (ts)(see FIG. 2)Between 1st pulse and 2nd pulsexyyBetween 2nd pulse and 3rd pulsexyN/ABetween 3rd pulse and 4th pulse2x + tsN/AN/ABetween 4th pulse and 5th pulsexN/AN/ABetween 5th pulse and 6th pulse0.35 to 1.30 sN/AN/ABetween 6th pulse and 7th pulsexN/AN/ABetween 7th pulse and 8th pulsexN/AN/ABetween 8th pulse and 9th pulse2x + tsN/AN/ABetween 9th pulse and 10th pulsexN/AN/ATime between bursts2.5 to 15.0 s2.5 to 30.0 s>15 sor not repeatedAmplitude difference betweenMaximum 10 dBMaximum 10 dBMaximum 10 dBtwo arbitrary pulses
TABLE 4Melody alarmCauseMedium priorityHigh priorityGeneralcccccc-ccHeartcegceg-gCArtificial perfusioncf#ccf#c-cf#Ventilationcafcaf-afOxygenCbaCba-gfTemperature/energy supplycdecde-fgSupply of medicine or liquidCdgCdg-CdFailure of apparatus or supplied productCccCcc-Cc
As described above, the high priority, medium priority, and low priority which are alarm condition priorities in the alarm standard for a biological information apparatus (ME apparatus) are defined in detail based on the risk management process (ISO 14971) shown in Table 1, and visual and auditory alarms which are output forms of the priorities are determined in accordance with the alarm priorities.
An example of a biological information monitoring apparatus which announces an alarm by means of an auditory sound and/or visual indicator will be described with reference to FIG. 1.
FIG. 1 is an external view of a biological information monitoring apparatus of the station type which is placed in a nurse's station or the like, and in which biological signals of a plurality of patients can be simultaneously monitored.
In FIG. 1, 1 denotes the biological information monitor of the station type, and 2 denotes a display screen on which numerals and waveforms that are obtained as a result of processing biological signals of a plurality (in the illustrated apparatus, eight) of patients are simultaneously displayed (in the illustrated state, only four patients are monitored).
The reference numerals 3-1, 3-2, and 3-3 denote display output portions for a visual alarm. The display output portions 3-1, 3-2 are individual display portions which can perform displays respectively corresponding to individual patients, and the display output portion 3-3 is a common display portion which is common to all patients. Each of the display portions is configured by, for example, LEDs, and selectively displays red, yellow, cyan light, or like alarm light in accordance with the alarm priority. In the display screen 2, furthermore, a visual alarm may be displayed in the display regions respectively corresponding to individual patients.
The reference numeral 4 is a speaker which outputs an auditory alarm. The speaker can output an alarm corresponding to the alarm priority by means of different frequencies, duration times, and the like.
In the above-described pulse oximeter, for a saturation alarm, the integral of the amount by which the oxygen saturation exceeds the upper threshold or falls below the lower threshold is calculated. When the integral exceeds the predetermined value, the saturation alarm is produced.
Until the saturation alarm is produced, therefore, the exceeding (falling) amount is integrated. Therefore, an influence due to noise or signal artifact is eliminated. When the saturation alarm is once produced, however, the saturation alarm is not cancelled unless the oxygen saturation returns to the upper threshold or lower, or to the lower threshold or higher.
In such a state where, after the saturation alarm is once produced, the oxygen saturation remains stagnant in the vicinity of the upper or lower threshold, the saturation alarm is not cancelled, and the alarm announcement in the constant audio and/or visual form is continued, so that there arises a possibility that the observer becomes accustomed to the alarm and overlooks a serious abnormality.
In the integration, in the case where, because of an unexpected phenomenon or the like, the oxygen saturation largely falls below the low sat threshold in a very short time and the saturation alarm is once produced, even when the phenomenon is improved and the oxygen saturation returns to the vicinity of the threshold, the priority is maintained.
In this case, although an alarm which has a low priority is originally generated, an emergency alarm is output, thereby causing a possibility that such an alarm interferes with the work of a medical person.
In the alarm standard for a biological information apparatus (ME apparatus), as described above, the high priority, the medium priority, and the low priority are visual and auditory alarms which are defined in detail based on the risk management process (ISO 14971) shown in Table 1. Consequently, there is a problem in that, in the case where a visual or auditory alarm (particularly, the low priority or the medium priority) is continued, it can become overlooked if it becomes prolonged.
Specifically, in a state where the oxygen saturation stagnates in the vicinity of the upper or lower threshold (the medium priority), the same priority is maintained, and hence the alarm announcement in the constant audio and/or visual form is continued as indicated in above-described Tables 1 to 4. Consequently, there is a possibility that a serious abnormality is overlooked because of accustomed recognition of the observer that the priority remains unchanged.
A generation of a technical alarm means that a failure of a biological signal measuring apparatus itself, a state where checking of a probe or detection of a pulse wave is disabled, or the like occurs. However, this is not directly related to a phenomenon in which an abnormality is caused in the biological signal of the patient. Even when a technical alarm is generated by an operation of a body motion of the patient such as separation of an electrode or a probe, it is often the case that restoration is immediately performed. Therefore, there is a possibility that the alarm is overlooked with a sense of expectance of recovery.